1. Technical Field
The subject matter disclosed herein relates generally to gas turbine engines and, more particularly, to repair of turbine nozzle segments found in gas turbine engines such as aircraft engines.
2. Description of Related Art
A gas turbine engine includes a compressor that pressurizes air and delivers the pressurized air to a combustor. In the combustor, the air mixes with fuel and ignites to generate hot combustion gases. The combustion gases flow downstream to a turbine section, which transforms energy of the combustion gas flow to power the compressor and to provide useful work. An example of such gas turbine engines is an aircraft engine that can power an aircraft in flight.
Aircraft engines may include stationary turbine nozzles that modify the gas flow and pressure within the turbine section. These changes can enhance engine performance. In one example, the aircraft engine has multiple turbine sections (or “stages”), where turbine nozzles channel the combustion gases that enter each turbine stage into a turbine rotor that is downstream of the turbine nozzle.
Turbine nozzles may comprise multiple segments that annularly bound the periphery of the turbine section. Each of the segments may have one or more vanes, which extend radially between arcuate bands that define a path through which the hot combustion gases flow. In one example, the segments mount to the engine casing in an annular array between the rotor blades of adjacent stages.
Operation of the aircraft engine exposes the turbine nozzles (and, accordingly, the nozzle segments) to a gas stream with properties (e.g., temperature) that can limit the effective service life of these components. Accordingly, the nozzle segments may comprise certain materials such as high temperature cobalt or nickel-based superalloys and may have coatings that comprise corrosion and/or heat resistant materials. In some cases, the aircraft engine may direct cooling air from the compressor onto the nozzle segments to prolong service life. However, even with such efforts, portions of the nozzle segments, particularly the vanes, can crack, corrode, and otherwise degrade. Such deterioration may require service to repair or to replace one or more of the nozzle segments to maintain safe and efficient operation.
The turbine nozzles are complex and intricate elements of the turbine engine. These elements are often made of relatively expensive materials, and may be expensive to manufacture. Thus, repair of the turbine nozzles is favored whenever possible. Some repairs focus on the cracks and restore the dimensional integrity of the vanes. Local distortion and under minimum wall thicknesses may reduce the success of these repairs, however, particularly when the problematic vane is subject to multiple repair processes. Often damage to the turbine nozzles prevents repair altogether.